New Delhi — When George Shultz touches down on this subcontinent Wednesday, the mere fact that he is arriving is considered significant by all sides. It has been 51/2 years since an American secretary of state has visited India , and more than three years since former national security adviser Zbigniew Brzezinski visited Pakistan.
Mr. Shultz will find a somewhat different situation in South and East Asia than existed when Washington's foreign policy makers were last here. There have been new shifts and alignments:
* There has been a thaw in relations between India and Pakistan, even though it is barely perceptible.
* Negotiations are under way in Geneva aimed at sending Soviet troops home from Afghanistan. Some 105,000 Soviet troops are there at present.
Thus, although bilateral relations will be discussed, including the airing of some thorny issues in both New Delhi and Islamabad, Mr. Shultz's talks are expected to focus on broader regional concerns.
He will find ready listeners - and probably even more ready talkers - in both India's Prime Minister Indira Gandhi and Pakistan's President Gen. Mohammad Zia ul-Haq. The two South Asia leaders basically distrust each other. Thus, when American spare parts for India's Tarapur nuclear power plant are discussed this week, there will be a predictable reaction across the frontier.
When Mr. Shultz is reminded that Pakistan would like more F-16s, Mrs. Gandhi, herself building up a formidable military arsenal, is bound to react.
But he will also find the two leaders interested in winning new foreign friends; both Mrs. Gandhi and General Zia have concentrated more on foreign than on domestic affairs. Mrs. Gandhi, as chairman of the nonaligned movement, has shown greater flexibility toward China and has begun diversifying India's sources of arms away from the Soviet Union, which has long been India's primary source.
General Zia, virtually encircled by unfriendly nations - India, Afghanistan, and Iran - has softened his approach to the Afghanistan negotiations and has been far less strident in denunciations of Moscow.
Afghanistan is, in fact, one area on which India and Pakistan share common concerns. Their views are not always shared by Washington, however. And according to authoritative sources both here and in Islamabad, there has long been a shared suspicion that the Reagan administration was willing to overlook instability in East Asia in favor of larger geopolitical concerns.
At the first meeting of the newly formed Indo-Pakistani joint ministerial commission, held early this month, far more time was spent discussing Afghanistan, according to those present, than in discussing outstanding bilateral disputes.
If the Soviet Union agrees to a specific timetable for withdrawing its troops , if Pakistan's 3 million Afghan refugees are permitted to go home, if the permanent members of the UN Security Council agree to act as guarantors, then Pakistan appears ready to accept a communist government in Kabul, though not necessarily that of Babrak Karmal.
This shift in attitude has been welcomed by New Delhi, which has long let it be known that it did not view warmly the prospect of an Islamic fundamentalist government in Afghanistan.
Thus, on this issue, the American secretary of state may find a rare unanimity between the two neighbors who have fought three wars. But India and Pakistan have a long way to go before the hostility is buried.
It is thus hoped that before Mr. Shultz's arrival, the contentious issue of the supply of spare parts for the American-built Tarapur plant can be resolved. Washington's agreement to allow France to supply the plant with nuclear fuel was a major accomplishment of Mrs. Gandhi's visit to Washington last summer. Eleventh-hour efforts are under way to find a suitable third country - probably West Germany or Italy, according to authoritative accounts - to provide the spare parts India claims are urgently needed to prevent radiation-contamination hazards at the plant.
The supply of spare parts can be made only in conformity with the US Nuclear Nonproliferation Act of 1978, which prohibits the resupply of fuel because of India's refusal to accept full international inspection of all its nuclear sites.
It is thus hoped in New Delhi that another third-country arrangement can be forged, and that the issue will not have to go before the US Congress, which could open a wide-ranging debate on both India's and Pakistan's refusal to sign the nuclear Non-Proliferation Treaty, and their ongoing flirtation with nuclear arms.
New conventional arms purchases will, however, be discussed in both Pakistan and India, but no agreements are likely as a result of the visit of Secretary Shultz. Pakistan is already receiving the first of 40 F-16s, along with $3.2 billion in US economic and military aid over the next few years.
India has been quietly discussing the purchase of American weaponry, including the C-130 aircraft, for nearly a year. But thus far there has been no decision, and simultaneous arms discussions with Britain, Germany, and France are continuing.
And, perhaps not fortuitously, the Indian defense minister, Ramaswamy Venkataraman, left for the Soviet Union on the eve of Mr. Shultz's visit here. He was to return yesterday, just in time to participate in the discussions as a leading member of Mrs. Gandhi's team.